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An airflow over the wing is causing the downwash at the end of the
airfoil. The airflow below the wing is now kind of captured between
the airfoil and the layer(s) of air underneath itself.

In this situation it can go in just two directions, up or down, The
majority of the flow will go down, bu a tiny fraction of the
molecules has to go up. If the number of molecules that go up is high
enough it will lift the airfoil up with it.

This is really what DaVinci already had discovered back in
1530-something.

Which is why he never flew. See the argument about "bullets" in the
link provided, above.

In the case of the airflow below the wing, it's not really "trapped".
It gets out of the way, below. Also, consider the wing of a B-52. I
believe it is entirely possible that a wing such as that on the B-52
can have a lower surface that is parallel to the airflow, but still
provides lift. That's because it's _mostly_ (or entirely) the
"sucking" action above the wing that contributes the most to lift.